This is one way to do it: In [1]: import numpy as np In [2]: from astropy import units as u In [3]: from astropy.coordinates import SkyCoord, FK4, FK5, Galactic In [4]: clra = np.zeros(3) In [5]: cldec = np.zeros(3) In [6]: c1 = SkyCoord(clra * u.deg, cldec * u.deg,...

What makes you think you can pass a tuple of tags to canvas.coords? As you can read on effbot.org, The New Mexico Tech website and in the Tk Manual you can pass an id or a tag. It will then return the coordinates of the first matching item or you...

First find the angle between the mouse point and center of circle Then calculate the needed point using that angle and radius of circle To find the angle: var diffX = mouseX - centerX; var diffY = mouseY - centerY; var angle = Math.atan2(diffY, diffX); To find the new...